Touch systems are well known in the art and typically include a touch screen having a touch surface on which contacts are made using a pointer such as for example a pen tool, finger or other suitable object. Pointer contacts with the touch surface are detected and are used to generate output pointer position data representing areas of the touch surface where pointer contacts are made.
International PCT Application No. PCT/CA01/00980 filed on Jul. 5, 2001 and published under number WO 02/03316 on Jan. 10, 2002, assigned to SMART Technologies Inc., assignee of the present invention, discloses a passive camera-based touch system. The camera-based touch system comprises a touch screen that includes a touch surface on which a computer-generated image is presented. A rectangular bezel or frame surrounds the touch surface and supports digital cameras at its corners. The digital cameras have overlapping fields of view that encompass and look across the touch surface. The digital cameras acquire images of the touch surface from different locations and generate image data. The image data is processed by digital signal processors to determine if a pointer exists in the captured image data. When it is determined that a pointer exists in the captured image data, the digital signal processors convey pointer characteristic data to a master controller, which in turn processes the pointer characteristic data to determine the location of the pointer in (x,y) coordinates relative to the touch surface using triangulation. The pointer location data is conveyed to a computer executing one or more application programs. The computer uses the pointer location data to update the computer-generated image that is presented on the touch surface. Pointer contacts on the touch surface can therefore be recorded as writing or drawing or used to control execution of an application program executed by the computer.
Although this camera-based touch system works extremely well, it has been found that when the digital camera frame rates are high, in less favorable light conditions, the ability to determine the existence of a pointer in the captured image data is diminished. As a result, there exists a need to improve the lighting environment for the digital cameras to ensure high resolution irrespective of ambient lighting conditions.
U.S. patent application Ser. No. 10/354,168 to Akitt et al. entitled “Illuminated Bezel And Touch System Incorporating The Same”, assigned to SMART Technologies Inc., assignee of the present invention, discloses an illuminated bezel for use in the above-described camera-based touch system. The illuminated bezel projects infrared backlighting across the touch surface that is visible to the digital cameras. As a result, when no pointer is positioned within the fields of view of the digital cameras, the digital cameras see bright bands of illumination as a result of the projected backlighting. When a pointer is positioned within the fields of view of the digital cameras, the pointer occludes the backlight illumination. Therefore, in each captured image the pointer appears as a high-contrast dark region interrupting the bright band of illumination allowing the existence of the pointer in the captured image to be readily detected.
Although the illuminated bezel works very well, because the illuminated bezel completely surrounds the touch surface and makes use of an array of infrared light emitting diodes mounted on a printed circuit board that is disposed behind a diffuser, manufacturing costs are significant especially in cases where the illuminated bezel surrounds large touch surfaces. As will be appreciated, lower cost backlight illumination for touch systems of this nature is desired.
Also, although the existence of the pointer in captured images can be readily detected, currently the use of monochrome digital cameras to capture images increases costs and provides limited information concerning attributes of the pointer used to contact the touch system.
It is therefore an object of the present invention to provide a novel apparatus for detecting a pointer within a region of interest.